This invention relates to wheel balancers and in particular to improved drive systems, safety circuitry, and displays working in conjunction with said drive systems for wheel balancers.
The determination of unbalance in vehicle wheels is carried out by an analysis with reference to phase and amplitude of the mechanical vibrations caused by rotating unbalanced masses in the wheel. The mechanical vibrations are measured as motions, forces, or pressures by means of transducers, which convert the mechanical vibrations to electrical signals. Each signal is the combination of fundamental oscillations caused by imbalance and noise.
It is believed that the drive systems for currently available balancers could be improved to aid in operation. For example, prior art balancers typically require the operator to manually rotate the wheel/tire assembly to the desired position for weight placement and/or runout correction. These balancers then use a manual brake or the motor itself to temporarily hold the shaft in the desired position. However, such a system could be improved. Manual rotation to the desired position is less than satisfactory since it requires the operator to interpret the balancer display correctly. Moreover, manual rotation itself is not desirable, since it ties up the operator""s time and attention. In conventional systems, however, the balancer motor cannot be used to rotate the wheel/tire assembly to the correct position since available motor controllers used in balancers are incapable of performing this function.
Using the motor itself to provide a braking action is not completely satisfactory either. Such braking is normally accomplished by applying rectified alternating current to an AC motor. This method is inherently subject to error. The actual stopping position may be incorrect if the tire is larger than average or turning too fast for the xe2x80x9cbrakexe2x80x9d to respond. Moreover, although currently available motor braking systems stop the wheel in approximately the correct position, they do not actual hold the tire in position since the motor would heat up if the xe2x80x9cbrakexe2x80x9d was left on. With conventional equipment, a wheel/tire assembly with sufficient static imbalance to overcome its own inertia, therefore, can roll away from the braked dynamic weight position as soon as the braking energy is released. In addition, electrical braking systems are usually of little use when power is removed from the circuit, as could occur should a power failure take place.
Currently available balancers could also be improved in another way. Presently, the balancer shaft position is sensed and the resulting signal is supplied to the control circuit. The control circuit typically analyzes the signal using software to determine if certain conditions (excessive rpm, excessive acceleration, etc.) exist. These systems are not foolproof, and could be improved.
Even when a wheel/tire assembly is balanced, non-uniformity in the construction of the tire as well as runout in the rim can cause significant vibration forces as the wheel rolls under vehicle load. Most tire manufacturers inspect their tires on tire uniformity machines and grind rubber off the tires as required to improve rolling characteristics of the tires. Even after this procedure, tires will often produce vibration forces (not related to imbalance) of 20 pounds as they roll on a smooth road. To put this in perspective of balancing, a 0.8 ounce balance weight is required to produce a 20 pound vibration force on a typical wheel traveling at 70 mph.
Prior art balancers are also not well equipped to take into account and correct for variations in uniformity of the wheel rim and the tire. It would be desirable, for example, to place a measured amount of imbalance in a wheel to counter tire non-uniformity forces or to detect and mark the position on a tire which should be matched to a corresponding position on the rim to reduce vibration due to non-uniformity of either or both. To the extent that presently available balancers do measure rim and tire runout, it is believed that the information they acquire is not particularly useful to the operator. In particular, presently available balancers which do measure runout generally display that runout to the user in the form of sine waves referenced to some arbitrary point. For a conventional system, which typically measures radial runout of both rims, this results in two (basically incomprehensible) sine waves. Such a system could be improved.
Many conventional balancers also assume that the wheel/tire assembly which is suitably balanced under an essentially no-load condition will also be suitably balanced when installed on the vehicle and subjected to the substantial load represented by the weight of the vehicle. This assumption is not valid under all conditions. It would be preferable in many circumstances to simulate loaded conditions to improve the results of the balancing operation.
Among the various objects and features of the present invention is a wheel balancer with improved performance.
Another object is the provision of such a wheel balancer which is capable of simulating loads on the wheel/tire assembly.
A third object is the provision of such a wheel balancer which is capable of determining loaded radial runout of the wheel/tire assembly.
A fourth object is the provision of such a wheel balancer which facilitates the remounting of a tire on a wheel to reduce imbalance.
A fifth object is the provision of such a wheel balancer which facilitates the matching of a tire and rim to reduce tire vibration.
A sixth object is the provision of such a wheel balancer which conveniently measures rim and tire runout and compares those values with specifications.
A seventh object is the provision of such a wheel balancer with controllable balancer torque which improves starting and running characteristics.
Other objects and features will be in part apparent and in part pointed out hereinafter.
In a first aspect of the present invention, a wheel balancer includes a shaft adapted for receiving a wheel/tire assembly, said shaft having a longitudinal axis and being rotatable about said axis so as to rotate a wheel/tire assembly removably mounted thereon. A rotation sensor assembly measures rotation of the shaft about its longitudinal axis, and a motor is operatively connected to the shaft for rotating said shaft about its longitudinal axis, thereby to rotate the wheel/tire assembly. A vibration sensor assembly measures vibration of the wheel/tire assembly as the wheel/tire assembly is rotated, and a load roller applies a generally radial force to the wheel/tire assembly during rotation of said wheel/tire assembly. Movement of the load roller is measured to determine loaded radial runout of the wheel/tire assembly while the force is applied thereto, and a tire stiffness value for the wheel/tire assembly is provided. A control circuit is responsive to the measured vibration of the wheel/tire assembly to determine wheel imbalance, and responsive to the determined imbalance, the measured loaded radial runout of the wheel/tire assembly, and the tire stiffness to determine the locations and magnitudes of correction weights to add to the wheel/tire assembly to reduce the vibration of the wheel/tire assembly when mounted on a traveling vehicle.
In a second aspect of the present invention the wheel balancer includes means for measuring movement of the roller to determine the loaded radial runout of the wheel/tire assembly while the force is applied thereto, and means for measuring the runout of the wheel rim of the wheel/tire assembly at the bead seat. A control circuit is responsive to the measured vibration of the wheel/tire assembly to determine wheel imbalance, responsive to the measurements of wheel rim runout, and responsive to the measured loaded radial runout of the wheel/tire assembly to determine an angular remount position of the tire on the rim to minimize some predetermined uniformity parameter of the wheel/tire assembly. An indication is provided to the user of the angular remount position of the tire with respect to the rim which would minimize the predetermined uniformity parameter of the wheel/tire assembly. An input means provides information identifying the vehicle or the class of vehicle on which the wheel/tire assembly is to be mounted, said control circuit having stored therein rim, tire and wheel/tire assembly specifications for a plurality of vehicles or vehicle classes, said control circuit comparing the specifications for a selected vehicle or vehicle class to the measured rim, tire and wheel/tire assembly uniformity values and selectively causing the display of messages to an operator relating to the results of the comparison.
In a third aspect of the present invention, the wheel balancer also includes means for obtaining a tire stiffness value for the wheel/tire assembly, said control circuit being responsive to the determined imbalance, the measured loaded radial runout of the wheel/tire assembly, and the tire stiffness to determine the locations and magnitudes of correction weights to add to the wheel/tire assembly to reduce the vibration of the wheel/tire assembly when mounted on a traveling vehicle.
In a fourth aspect of the present invention, the wheel balancer also includes input means for providing information identifying the vehicle or the class of vehicle on which the wheel/tire assembly is to be mounted, said control circuit having stored therein rim, tire and wheel/tire assembly specifications for a plurality of vehicles or vehicle classes, said control circuit comparing the specifications for a selected vehicle or vehicle class to the measured rim, tire and wheel/tire assembly uniformity values and selectively causing the display of messages to an operator relating to the results of the comparison.
In a fifth aspect of the present invention, the wheel balancer includes means for holding the load roller fixed rigidly in position, and sensors for measuring the force variation as the wheel/tire assembly is rotated and for measuring imbalance vibrations of the wheel/tire assembly as the wheel/tire assembly is rotated. The control circuit is responsive to the measured vibration of the wheel/tire assembly to determine wheel imbalance and responsive to the force variation measurements to determine the locations and magnitudes of correction weights to add to the wheel/tire assembly to reduce the vibration of the wheel/tire assembly when mounted on a traveling vehicle.
In a sixth aspect of the present invention, the wheel balancer includes a control circuit for controlling the application of power to the motor, said control circuit being connected to the sensor assembly and being responsive to the measured rotation of the shaft and to software instructions stored in a memory to control a parameter of the rotation of the wheel/tire assembly, said parameter being selected from a group consisting of direction of rotation of the wheel/tire assembly, speed of rotation of the wheel/tire assembly, and torque applied to the wheel/tire assembly, said control circuit substantially continuously monitoring position and rotation rate of the shaft and substantially continuously adjusting power to the motor.
In a seventh aspect of the present invention, the wheel balancer includes a control circuit for controlling the load roller to press against the wheel/tire assembly during at least three complete revolutions of the wheel/tire assembly, said control circuit after said at least three complete revolutions controlling the load roller to separate from the wheel/tire assembly, said control circuit being responsive to measurements from the vibration sensor assembly once the load roller is separated from the wheel/tire assembly.
In an eighth aspect of the present invention, the wheel balancer includes means for measuring movement of the load roller to determine the effective diameter of the wheel/tire assembly. The control circuit is responsive to the measured vibration of the wheel/tire assembly to determine wheel imbalance, and responsive to the measured effective diameter of the wheel/tire assembly to determine effective diameter of the wheel/tire assembly.
In a ninth aspect of the present invention, the wheel balancer includes a sensor for measuring the lateral force exerted between the load roller and the wheel/tire assembly. The control circuit is responsive to the measured vibration of the wheel/tire assembly to determine wheel imbalance, and responsive to the measurement of lateral force to indicate to the user a message relating to the measured lateral force.
In a tenth aspect of the present invention, the wheel balancer includes means to set the desired magnitude of the force applied to the wheel/tire assembly by the load roller, the control circuit being responsive to the magnitude setting means to cause the load roller to apply a force of the desired magnitude to the wheel/tire assembly.